This invention generally relates to inflation devices used in medical procedures. More particularly, the present invention pertains to an inflation timing system suitable for inflating and deflating catheter balloons used in vascular procedures such as angioplasty performed on a patient for maintaining the patency of a blood vessel.
Dilatation balloon catheters have been used in increasing numbers in angioplasty procedures to dilate or enlarge blood vessels that have been partially or almost completely blocked by stenosis (a narrowing of the vessel due to injury or disease). Angioplasty procedures have been used to treat stenoses in coronary arteries, peripheral arteries, urethral passages, fallopian tubes, etc. Particularly, the procedure for dilating coronary arteries, referred to as percutaneous transluminal coronary angioplasty (PTCA), has provided an effective and less traumatic treatment technique than coronary by-pass surgery or other surgical treatment methods.
In a typical PTCA procedure, a guiding catheter is percutaneously introduced into the vascular system of a patient and is directed to a point near the site of the occlusion. Subsequently, a guidewire and a dilatation catheter having an inflatable balloon on the distal end thereof are introduced through the guiding catheter with the guidewire slidably disposed within an inner lumen of the dilatation catheter (commonly referred to as an over-the-wire system). The guidewire is advanced out of the distal end of the guiding catheter and is maneuvered into the patient's vasculature containing the lesion to be dilated, and is then advanced beyond the lesion. Thereafter, the dilatation catheter is advanced over the guidewire until the dilatation balloon is located across the lesion. Once in position across the lesion, the balloon of the dilatation catheter is filled with radiopaque liquid at relatively high pressures (e.g., generally greater than about 4 atmospheres) and is inflated to a predetermined size, preferably the same as the inner diameter of the artery at that location. The inflated balloon radially compresses the atherosclerotic plaque of the lesion against the inside of the artery wall to thereby dilate the lumen of the artery and allow blood to flow freely therethrough. In a typical PTCA procedure, the balloon may be inflated and deflated several times, with the pressure maintained for a short duration, i.e., typically three minutes or less during each inflation, until the desired patency in the blood vessel is obtained. The balloon is then deflated so that the dilatation catheter can be removed and blood flow resumed through the dilated artery. The above PTCA procedure also can be performed using a fixed-wire system or a rapid exchange guidewire system.
To inflate or deflate the balloon, the physician typically uses an inflation system such as a syringe placed in fluid communication with the interior of the balloon. The physician uses one hand to grasp the syringe body and the other hand to maneuver the plunger to pressurize the inflation fluid. Syringe-type inflation systems of the type described are manufactured and sold by Advanced Cardiovascular Systems, Inc. of Santa Clara, Calif. under the trademark INDEFLATOR.
There are some drawbacks associated with a manual inflation procedure such as the one described. For example, each time the physician wants to adjust or change the location of the balloon in the artery, she must use her hand alternatingly on the proximal end of the catheter for maneuvering the balloon to the desired location and on the inflation device for pressurizing or depressurizing the balloon. Rather than switching hands between the balloon catheter and the inflation device, it is desirable for the physician to be able to simultaneously control the inflation pressure and the location of the balloon in the artery. Another drawback of manual inflation systems is that the physician may experience hand fatigue as a result of operating an inflation device for several inflation and deflation cycles during an angioplasty procedure. Additionally, manual inflation devices are often bulky, especially compared with the size of a dilatation balloon catheter which is small and delicate. The presence of a bulky inflation device is preferably to be avoided in the immediate area of a balloon dilatation catheter so that the physician retains the proper "feel" of the catheter without interference from the weight and size of the inflation device.
In addition to the above concerns, it is desirable for the physician performing an angioplasty procedure to monitor the balloon pressure and the time of the inflation and deflation cycles. A balloon pressure display allows the physician to monitor whether the arterial plaque causing the stenosis is subjected to a sufficiently high pressure to cause compression of the plaque. Also, the physician would like to monitor the balloon pressure to estimate the resultant diameter of the balloon, and to ensure that the balloon pressure limits specified by the manufacturer are not exceeded so as to cause a balloon failure. In case the balloon pressure suddenly changes, the pressure display can alert the physician of the possibility of some failure either of the artery or of the catheter itself. Furthermore, it is desirable for the physician to monitor the elapsed time of each inflation and deflation cycle and the total inflation and deflation times so as not to deprive the patient of blood flow inside the artery beyond acceptable time periods. Early model inflation systems provided balloon pressure measurements by utilizing analog pressure gauges to correlate the force applied on the inflation device with the pressure inside the balloon.
In recent years, various inflation devices have become known which are able to instantaneously monitor, display, and record balloon pressure values and inflation times. Other advances in the design of inflation systems have been directed to creating automated inflation devices, whereby a microprocessor provides control signals to a drive unit which advances or retracts a syringe for the purpose of inflating or deflating a balloon catheter. The microprocessor can be made to follow a predetermined output pattern based on the inflation pressure detected by the pressure transducer and the time of inflation, or it can be designed for manual activation by control switches that are typically mounted on the same unit that displays the pressure and time values. Some of the automated inflation devices include a floor switch for operating a control unit to inflate and deflate the balloon. There are some disadvantages in connection with floor switches, such as the possibility of activation of the control unit by catheter lab personnel who may inadvertently step on the floor switch.
Further, such inflation devices reduce the hands-on control of a physician who may desire to inflate or deflate the balloon catheter at a precise moment during the maneuvering of the catheter in the artery. Activation of control switches that are typically mounted away from the balloon catheter requires the physician to give up control of the proximal end of the catheter in order to activate the control switches. Thus, existing inflation systems do not lend themselves to simultaneous activation of the inflation device and timing controls by the physician.
Another important step that takes place in a typical angioplasty procedure is the priming of the inflation system and the prepping of the balloon. The physician performing an angioplasty procedure must rid the inflation system and the balloon from air bubbles before the insertion of the catheter inside the patient's vasculature. If the system is not primed and prepped, these air bubbles enter the inflation lumen of the catheter and create unwanted pockets of space in the balloon that may interfere with the balloon inflation. Current methods of priming are well known in the art by angioplasty practitioners, and typically require the physician to manually inflate and deflate the system several times until the air bubbles disappear. After the priming function has been completed, the pressure in the inflation lumen and the inflation balloon may be less than zero. Thus, when an automatic pressure measuring device is used in conjunction with a timer, false or inaccurate inflation times (artifactual inflation) might be recorded since the balloon pressure starts out at a negative pressure.
What has been needed and heretofore unavailable is a simplified automated inflation system that enables the physician to effectively, easily, and simultaneously control and monitor the inflation pressure and the inflation and deflation time of the balloon member. Such an inflation system would be able to easily interface with commercially available dilatation balloon catheters, and would eliminate the need for having bulky components of an inflation system in the immediate area of an angioplasty procedure. Also, such an automated inflation system would be able to monitor and display information relating to balloon pressure and inflation times.